Minerals, such as kaolin, in their crude or unprocessed state inherently contain a variety of impurities that are unique and specific to the deposit. In response to needs in agriculture, the present invention is directed to the water processing of highly impure to slightly impure minerals to make them useable, functional, improved in performance, and generally safer for agricultural particle film depositions. This processing is commonly referred to as either water processing or water washing in the mineral industry.
Kaolin clay, for example, generally uses two different processing methods to produce a “beneficiated”, marketable material. These methods are commonly referred to as dry processing and wet processing. The dry process method generally produces a product that closely mirrors the properties originally found in the crude kaolin. Because of this, final products containing the desired particle size distribution, having low abrasivity, and having elevated brightness are typically determined by reliance on the quality of the deposit as determined by testing of the drilled core samples. With dry processing, the crude kaolin is simply crushed, dried, pulverized, and air floated to remove coarse grit particles.
A more recent development has been the wet processing method to produce higher quality products of more uniform and predetermined physical and chemical properties, which are less reliant on crude selection. Therefore, crude kaolins of widely varying ore quality may now be used to produce products which are more uniform and of higher marketable value. Because wet processing as a whole encompasses an extensive array of beneficiation processes, the final product can also vary with respect to the degree of quality, characteristics, and performance. Wet processing also allows for ease of manipulation of crude source and adjustment of final quality specification.
As disclosed at www.kaolin.co.za, or by testing, water-washed kaolin from Serina Kaolin in South Africa referred to as Serina Filler Grade may be used as a pesticide carrier. A finer particle size product called Serina Ultrafine is listed for paint, rubber, and ceramic applications but not for pesticide carrier use. In the following Table 1, the Serina properties are summarized.
TABLE 1MeanResidue OnparticleTradeCrystallineParticle45 MicronEinlehnerElrephosize, psdNameSilica (%)SizeScreen (%)AbrasionBrightnesspH(microns)Serina0.5848% less0.203583%52.1 Fillerthan 2Grade - UmicronsSerina3.0448% less0.203583%52.62Fillerthan 2Grade - NmicronsSerinaNot listed70% less0Not listed83%4-5Not listedUltrafineor testedthan 2or testedor testedmicrons
The processing noted for the Serina products indicates a minimum level of water processing (beneficiation) as indicated by the properties shown. The particle size has not been made finer than 70%<2 microns. This is considered to be coarse by water processing standards as marketed for decades, for example, by kaolin producers in Georgia, USA, Brazil, and the United Kingdom for many uses. The 45 micron screen residue for the Filler Grade is 0.2 and Ultrafine grade is noted as 0% which by implication of the significant figures indicates a range of 0.49% and lower. The brightness of both has not been raised above 83% indicating little or no brightness beneficiation. The Einlehner Abrasion of 35 for the Serina Filler grade is high versus water-processed kaolin used in paper and paints which generally is less than 10. The pH's of 5 or 4.0 to 5.0 is in the range of typical natural pH of kaolin in the ground and indicates that no pH adjustment was made and no alkaline (basic) or otherwise neutralizing additives are present. Neither tested grade, U or N (Comparative A below), has a crystalline silica content below 0.20%.
The website describes under “Refining Process” the following: Serina Filler grade: Wet milling, screening and hydrocyclone beneficiation followed by mechanical-thermal drying and Serina Ultrafine grade: Water washing, hydrocyclone beneficiation and screening followed by mechanical-thermal drying. These descriptions confirm a minimum level of water processing such as the use of hydrocyclones and screens and no utilization of commonly known state of the art processes. The products are both offered as powder and pellet form. No product in spray dried bead form is noted.
U.S. Pat. No. 4,738,726 teaches that a dispersant is used at 0.025 to 0.2% by weight based on the weight of the dry clay. The clay is used for coating paper.
U.S. Pat. No. 6,110,867 discloses the use of hydrous kaolin for application to horticultural crops for enhancing photosynthesis but no mention is made of the properties of the hydrous kaolin or the presence of a chemical additive. Kaolins that are substantially free of crystalline silica and low in titanium have been used as inert fillers, diluents, or adjuvants in low concentrations in wettable powder and dry flowable type agricultural sprays. Levels of kaolins used in these applications are sub-functional for effective use as agricultural particle films and, in addition, are not formulated to be effective particle films. For tree crops, for example, kaolin wettable powder and dry flowable chemical pesticide sprays are used at about 0.5-6 lbs per acre on medium sized trees. Vines and bushes usually require about half of these amounts and low-growing row crops about a fourth to half of these amounts. Maximum use of a kaolin wettable powder or dry flowable for very large trees using 200 gallons per acre of water would be about 12 lbs per acre. Kaolin typically makes up 80 to 95% of the composition but may be less as cited by commonly assigned U.S. Pat. No. 7,018,643B2 on Pesticide Delivery System. Kaolin wettable powder and dry flowable chemical pesticide sprays contain additives such as pesticides.
In comparison, agricultural particle films use much higher levels of mineral particles per given area of substrate. For example, a composition (95% kaolin and 5% “other”) called SURROUND® WP crop protectant is used as an agricultural particle film. Surround WP crop protectant instructs on its labels to use concentrations of 20.8 to 50 lbs per 100 gallons or 2.5 to 6% wt/wt in sprays. Per the directions for use, medium sized trees use 20.8 to 50 lbs per acre per spray. Vines and bushes usually require about half of these amounts, and low-growing row crops about a fourth to half of this amount. Use of Surround WP crop protectant for very large trees using 200 gallons per acre of water would be 50 to 100 lbs per acre.
Kaolin deposition difference between particle films and kaolin wettable powders or dry flowable type compositions can be considered by average theoretical application mass of mineral per given area of substrate. For example, for an orchard of 200 trees/acre, with the average leaf area of a single tree of 35m2, there would be about 14,000 m2 of leaf area for the entire orchard, including the top and bottom leaf surface. A 20.8 lb (19.76 lbs of kaolin mineral at 95%) application of Surround WP particle film, which is the minimum use level, calculates to an average theoretical kaolin deposition of about 63 ug/cm2. In comparison, the maximum average deposition level of mineral in a kaolin wettable powder or dry flowable type would have a deposition of about 15 to 18 ug/cm2. FIG. 1 shows SURROUND® WP crop protectant has undissolved particles; this means that chemical additive is not uniformly distributed among or on the main kaolin (as defined below).
Per the labeled application rate, a commercially available wax and bentonite agricultural product called Raynox delivers about 1 lb of bentonite mineral component per acre. (The labeled rate of Raynox is up to 2.5 gallons per acre. If the density of Raynox is 8 lbs per gallon at 5% mineral, this equals only 1 lb of bentonite per acre.) It is not known if the bentonite mineral component is wet processed. U.S. Patent Application Publication 2004/0146617 discloses the use of bentonite for application to fruits and vegetables.
Typical deficiencies associated with the non-water washing manufacturing process are a non-uniform and relatively coarse particle size distribution, moderate to poor optical properties in coatings, low brightness, and the presence of impurities such as crystalline silica, base metal oxides such as titanium oxides, naturally occurring salts, and trace heavy metals. Some impurities may be present in such a high concentration as to make the product unsafe and virtually unusable, one example being kaolin deposits found in Spain and other locations, which can contain up to ⅓ crystalline silica and are referred to as kaolinitic sand. Another example is Georgia, USA kaolin, which is relatively higher in purity, but may contain elevated levels of base metal oxides such as titanium dioxide.
It can generally be stated that the presence of crystalline silica impurities is considered highly undesirable due to the inherent abrasiveness of the material and for health and safety concerns which crystalline silica imposes. Coarse crystalline silica particle fractions are extremely hard and abrasive materials. When present at elevated levels and applied in high concentrations, such as in particle film applications, crystalline silica will cause unnecessary equipment wear and premature equipment failure. The added scouring effect which crystalline silica can cause on contact surfaces will also result in the unwanted delivery of dislodged contaminates such as toxic metals and the like. In addition, when formulated and delivered as an agricultural spray, the abrasive particle contaminates can produce wounding of the horticultural surface which may further result in decreased disease tolerance, decreased pest resistance and increased phytotoxicity. Fine crystalline silica particle fractions are undesirable because they are a pulmonary carcinogen and inhalation hazard and are typically not adequately removed through non-water washed, processing methods. IARC has classified crystalline silica as a carcinogen.
Typically, the sedimentary kaolin deposits found in the United States (Georgia and South Carolina), are considered to be of a higher crude quality as they contain lower levels of crystalline silica, are of a finer particle size distribution, are generally brighter, are relatively abundant and are found close to the surface allowing for ease of mining and recovery. One negative aspect of these kaolins is that they contain higher levels of titanium-based impurities. Titanium oxides can negatively affect color. Therefore, a less intense method of processing is necessary to remove the crystalline silica fraction which may be present, but special water processing steps are required to lower the levels of the base metal oxide. In addition, the removal of the titanium oxide impurities will generally increase the optical brightness of the finished material and produce a product containing a higher concentration of kaolin mineral.
Non-water-washed products are manufactured by drying, crushing, and milling crude minerals. In some, through air “floating” the useful fine particle segment is captured and the coarse product is discarded. Air floating has the ability to remove particles that are either greater in mass than the desired mineral or are not attached to the desired mineral. The resulting non-water washed product has a crystalline silica content from about 3 to about 36 weight percent. In the following Table 2, the properties of commercially available agricultural compositions comprising air processed kaolin are summarized and PSD stands for (average) particle size distribution.
TABLE 2+325Res-EinlehnerGECrystallineidue(mg/100kTiO2Bright-PSDTrade NameSilica (%)(%)rev)(%)ness(microns)CropWhite25.405.501720.3377.73.2Snow25.33.61880.3275.56.3Sunguard5.001.61302.0070.21.4Sombreador2.910.492320.4173.93.6M.A.F.A.36.199.302380.4174NALeroiaA.B.S.A. 454.428.602380.3074.44.1
It is common in many industries to use a chemical such as a surfactant to aid slurry handling and deposition properties. The chemical additive is dispersed in the slurry. In agriculture, a slurry of unrefined or air-floated minerals such as kaolin or calcium carbonate, or other minerals, have been commonly made by growers in spray tanks, often with a chemical dispersant added prior to application to a substrate. These compositions do not have the chemical additive “uniformly distributed among or on the functional particles” (as defined later).
SunBrite is a commercially available agricultural composition comprising a blend of limestone and titanium dioxide.
A commercial agricultural product called Raynox comprises primarily wax but it also has been found to contain hydrous kaolin that is not extensively processed and contains a high level of the surfactant and/or solvent morpholine.
A Material Safety Data Sheet from Columbia River Carbonates for Microna Shade calcium carbonate discloses that the limestone contains crystalline silica, typical levels are below 0.3 (w/w) in the product. No mention is made of the presence of a chemical additive.
One attractive agricultural particle film is provided by SURROUND® crop protectant available from Engelhard Corporation.